Method for controlling surface roughness in MEMS structure

Abstract

The present disclosure provides a method for manufacturing a CMOS-MEMS structure. The method includes etching a cavity on a first surface of a cap substrate; bonding the first surface of the cap substrate with a sensing substrate; thinning a second surface of the sensing substrate, the second surface being opposite to a third surface of the sensing substrate bonded to the cap substrate; etching the second surface of the sensing substrate; patterning a portion of the second surface of the sensing substrate to form a plurality of bonding regions; depositing an eutectic metal layer on the plurality of bonding regions; etching a portion of the sensing substrate under the cavity to form a movable element; and bonding the sensing substrate to a CMOS substrate through the eutectic metal layer.

What is claimed is: 
     
       1. A method for manufacturing a CMOS-MEMS structure, comprising:
 etching a cavity on a first surface of a cap substrate; 
 bonding the first surface of the cap substrate with a sensing substrate; 
 thinning a second surface of the sensing substrate, the second surface being opposite to a third surface of the sensing substrate bonded to the cap substrate; 
 etching the second surface of the sensing substrate while maintaining a planar profile of the etched second surface with a first roughness; 
 patterning a portion of the second surface of the sensing substrate to form a plurality of bonding regions and a plurality of recess bottoms, the plurality of recess bottoms having a second roughness, wherein the first roughness is controlled to be smaller than the second roughness; 
 depositing an eutectic metal layer on the plurality of bonding regions; 
 etching a portion of the sensing substrate under the cavity to form a movable element; and 
 bonding the sensing substrate to a CMOS substrate through the eutectic metal layer, 
 wherein the sensing substrate and the plurality of bonding regions are composed of undoped semiconductor material. 
 
     
     
       2. The method of  claim 1 , wherein etching the second surface of the sensing substrate comprises a wet etching operation, a dry etching operation, a polishing operation, or combinations thereof. 
     
     
       3. The method of  claim 1 , further comprising performing a Chemical Mechanical Planarization (CMP) on the plurality of bonding regions after patterning the portion of the second surface of the sensing substrate to form the plurality of bonding regions. 
     
     
       4. The method of  claim 1 , wherein thinning the second surface of the sensing substrate comprises performing a grinding operation. 
     
     
       5. The method of  claim 1 , wherein the eutectic metal layer comprises Ge, Al or copper. 
     
     
       6. The method of  claim 1 , wherein a roughness of the sensing substrate is in a range of 10 Å to 1000 Å after etching the second surface of the sensing substrate. 
     
     
       7. The method of  claim 1 , wherein the movable element is etched to move in at least one of the x-, y-, and z-directions. 
     
     
       8. The method of  claim 1 , further comprising an additional movable element adjacent to the movable element, wherein a pitch between adjacent movable elements is in a range of 1 μm to 10 μm and a width of the movable element surrounded by the adjacent bonding regions is in a range of 100 to 10000 μm. 
     
     
       9. A method for controlling a surface roughness of a CMOS-MEMS structure, comprising:
 etching a cavity on a first surface of a cap substrate; 
 bonding the cap substrate and a sensing substrate; 
 thinning a second surface of the sensing substrate opposite to a third surface of the sensing substrate bonded to the cap substrate; 
 etching the second surface of the sensing substrate to maintain a planar profile with a first roughness in a range of from 10 Å to 1000 Å; and 
 patterning a portion of the second surface of the sensing substrate to form a plurality of recess bottoms, each having a second roughness, 
 wherein the first roughness is controlled to be smaller than the second roughness. 
 
     
     
       10. The method of  claim 9 , wherein etching the second surface of the sensing substrate comprises a wet etching operation, a dry etching operation, a polishing operation, or combinations thereof. 
     
     
       11. The method of  claim 9 , further comprising patterning a portion of the second surface of the sensing substrate to form a plurality of bonding regions and subsequently performing a Chemical Mechanical Planarization (CMP) on the plurality of bonding regions. 
     
     
       12. The method of  claim 9 , wherein thinning the second surface of the sensing substrate comprises performing a grinding operation. 
     
     
       13. The method of  claim 9 , wherein etching the second surface of the sensing substrate comprises a wet-etchant comprising a base and an oxidant. 
     
     
       14. The method of  claim 13 , wherein the base comprises ammonium hydroxide (NH 4 OH), tetramethylammonium hydroxide (TMAH), and potassium hydroxide (KOH). 
     
     
       15. The method of  claim 13 , wherein the oxidant comprises hydrogen peroxide (H 2 O 2 ) and ozone (O 3 ). 
     
     
       16. A method for controlling a surface roughness of a CMOS-MEMS structure, comprising:
 etching a cavity on a first surface of a cap substrate; 
 bonding the cap substrate and a sensing substrate; 
 thinning the sensing substrate from a second surface opposite to a third surface bonded to the cap substrate; 
 etching the second surface right after the thinning the sensing substrate to achieve a first roughness; and 
 patterning a portion of the second surface of the sensing substrate to form a plurality of bonding regions and a plurality of recess bottoms, the plurality of recess bottoms having a second roughness, 
 wherein the first roughness is controlled to be smaller than the second roughness. 
 
     
     
       17. The method of  claim 16 , further comprising performing a chemical mechanical planarization operation over the plurality of the bonding regions. 
     
     
       18. The method of  claim 16 , wherein the first roughness is controlled to be in a range of from about 10 Å to 1000 Å. 
     
     
       19. The method of  claim 16 , wherein the etching the second surface comprises performing a wet etching operation comprising a base and an oxidant. 
     
     
       20. The method of  claim 16 , further comprising:
 depositing an eutectic metal layer over the plurality of bonding regions; and 
 patterning the plurality of recess bottoms to form movable elements.